This section is intended to introduce the reader to the diverse aspects of the art, which may be related to various aspects of the present invention which are described and/or claimed hereinbelow. This discussion is considered to be useful for providing the reader with background information so as to facilitate a better understanding of the various aspects of the present invention. Consequently, it must be understood that these statements must be read in this light, and not as an exposition of the prior art.
EP-A-0 644 411 in the name of the applicant describes a reflection or transmission deflectometry tool. This tool allows the measurement by reflection or transmission of the geometric structure of an optical component. The principle of such a measurement tool is to illuminate the optical component to be measured by a radiation of known wavefront—in the simplest case a plane wave—and to measure the wavefront after reflection or transmission on the optical component to be measured. Measurement of the wavefront after reflection or transmission makes it possible to derive the geometric characteristics of the component to be measured.
It is thus known to determine the geometry of one face of the component; the geometry of the other face of the component being assumed known for the calculations. A need therefore exists for a measurement tool which makes it possible to determine the various characteristics of an optical component, and in particular of its two faces. Such a tool makes it possible in particular to effectively measure progressive ophthalmic lenses, by determining in an exact manner the shape of each of their two faces and by perfectly positioning one face with respect to the other without having to formulate any assumption about one of these faces.
FR-2 813 391 A1, also in the name of the applicant, describes a method for measuring the geometric structure of an optical component implementing a pair of measurements in transmission of an optical component. But the precision of the geometric structure reconstructed is not always satisfactory because each of the two measurements combines the effects of the two faces traversed. Also known is DE102004047531, where two interferometric measurements are implemented, one in reflection, the other in transmission, to determine a surface topography and an internal distribution of refractive index of a live organism (cell or group of cells). But in an implicit manner, to achieve an absolute result, which makes it possible to translate the measurement of phase variation of a reflected or transmitted optical wave, into a map of heights or of variations of refractive index, the measurement described by this document requires a priori knowledge of the topography or of the refractive index distribution of the organism.
Moreover, it is known to measure the faces of an optical component with the aid of a gauge with mechanical or optical probe operating point by point, face by face or simultaneously at a point of each of the two faces. But the duration of a measurement of a face is significant and it is still always difficult to position the measurement of the first face with respect to the second face. Furthermore a point by point measurement in general requires extremely precise means for displacing a (mechanical or optical) probe which render it relatively expensive as regards acquisition and servicing and difficult to deploy in on an industrial site.